A conventional battery contains a number of components while the reported paper battery integrates all of the battery components in a single structure, making it more energy efficient. The battery contains carbon nanotubes, each about one millionth of a centimetre thick, which act as an electrode. The nanotubes are embedded in a sheet of paper soaked in ionic liquid electrolytes, which conduct the electricity. It is claimed that the flexible battery can function even if it is rolled up, folded or cut.